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gh-117657: Quiet erroneous TSAN reports of data races in _PySeqLock #117955

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Merged
merged 2 commits into from
Apr 17, 2024
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gh-117657: Quiet erroneous TSAN reports of data races in _PySeqLock #117955

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a9907b8
Quiet erroneous TSAN reports of data races in `_PySeqLock`
mpage Apr 17, 2024
778de8e
Merge branch 'main' into gh-117657-seq-lock
DinoV Apr 17, 2024
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Quiet erroneous TSAN reports of data races in _PySeqLock 
TSAN reports a couple of data races between the compare/exchange in
`_PySeqLock_LockWrite` and the non-atomic loads in `_PySeqLock_{Abandon,Unlock}Write`.
This is another instance of TSAN incorrectly modeling failed compare/exchange
as a write instead of a load.
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@mpage
mpage committed Apr 17, 2024
commit a9907b87d11810b615075671bc3105ba64c54176
6 changes: 3 additions & 3 deletions Python/lock.c
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Original file line number Diff line number Diff line change
Expand Up @@ -472,7 +472,7 @@ _PyRWMutex_Unlock(_PyRWMutex *rwmutex)

void _PySeqLock_LockWrite(_PySeqLock *seqlock)
{
// lock the entry by setting by moving to an odd sequence number
// lock by moving to an odd sequence number
uint32_t prev = _Py_atomic_load_uint32_relaxed(&seqlock->sequence);
while (1) {
if (SEQLOCK_IS_UPDATING(prev)) {
Expand All @@ -492,14 +492,14 @@ void _PySeqLock_LockWrite(_PySeqLock *seqlock)

void _PySeqLock_AbandonWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence - 1;
uint32_t new_seq = _Py_atomic_load_uint32_relaxed(&seqlock->sequence) - 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}

void _PySeqLock_UnlockWrite(_PySeqLock *seqlock)
{
uint32_t new_seq = seqlock->sequence + 1;
uint32_t new_seq = _Py_atomic_load_uint32_relaxed(&seqlock->sequence) + 1;
assert(!SEQLOCK_IS_UPDATING(new_seq));
_Py_atomic_store_uint32(&seqlock->sequence, new_seq);
}
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2 changes: 0 additions & 2 deletions Tools/tsan/suppressions_free_threading.txt
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Expand Up @@ -26,7 +26,6 @@ race:_PyObject_GC_IS_SHARED
race:_PyObject_GC_SET_SHARED
race:_PyObject_GC_TRACK
race:_PyType_HasFeature
race:_PyType_Lookup
race:assign_version_tag
race:compare_unicode_unicode
race:delitem_common
Expand All @@ -48,4 +47,3 @@ race:start_the_world
race:tstate_set_detached
race:unicode_hash
race:update_cache
race:update_cache_gil_disabled
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